Velocity progressive valving

ABSTRACT

A shock absorber has a valve assembly having a valve that is biased away from a valve body. A controlled restriction is defined between the valve and the valve body. During stroking of the piston of the shock absorber, the valve moves toward the valve body to close the restriction. The valve assembly can be used in the piston assembly, the base valve assembly or both.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.12/620,618 filed on Nov. 18, 2009. The entire disclosure of the aboveapplication is incorporated herein by reference.

FIELD

The present disclosure relates to automotive shock absorbers. Moreparticularly, the present disclosure relates to valve assembliesincorporated into the shock absorber which control the dampingcharacteristics for the shock absorber using velocity progressivevalving.

BACKGROUND

The statements in this section merely provide background informationrelated to the present disclosure and may not constitute prior art.

Shock absorbers are used in conjunction with automotive suspensionsystems and other suspension systems to absorb unwanted vibrations whichoccur during movement of the suspension system. In order to absorb theseunwanted vibrations, automotive shock absorbers are generally connectedbetween the sprung (body) and the unsprung (suspension/chassis) massesof the vehicle.

The most common type of shock absorbers for automobiles is the dashpottype which can be either a mono-tube design or a dual-tube design. Inthe mono-tube design, a piston is located within a pressure tube and isconnected to the sprung mass of the vehicle through a piston rod. Thepressure tube is connected to the unsprung mass of the vehicle. Thepiston divides the pressure tube into an upper working chamber and alower working chamber. The piston includes compression valving whichlimits the flow of damping fluid from the lower working chamber to theupper working chamber during a compression stroke and rebound valvingwhich limits the flow of damping fluid from the upper working chamber tothe lower working chamber during a rebound or extension stroke. Becausethe compression valving and the rebound valving have the ability tolimit the flow of damping fluid, the shock absorber is able to produce adamping force which counteracts the vibrations which would otherwise betransmitted from the unsprung mass to the sprung mass.

In a dual-tube shock absorber, a fluid reservoir is defined between thepressure tube and a reservoir tube which is positioned around thepressure tube. A base valve assembly is located between the lowerworking chamber and the fluid reservoir to control the flow of dampeningfluid. The compression valving of the piston is moved to the base valveassembly and is replaced in the piston by a compression check valveassembly. In addition to the compression valving, the base valveassembly includes a rebound check valve assembly. The compressionvalving of the base valve assembly produces the damping force during acompression stroke, and the rebound valving of the piston produces thedamping force during a rebound or extension stroke. Both the compressionand rebound check valve assemblies permit fluid flow in one direction,but prohibit fluid flow in an opposite direction; however, they aredesigned such that they do not generate a damping force.

The valve assemblies for the shock absorber have the function ofcontrolling oil flow between two chambers during the stroking of theshock absorber. By controlling the oil flow between the two chambers, apressure drop is build up between the two chambers and this contributesto the damping forces of the shock absorber. The valve assemblies can beused to tune the damping forces to control ride and handling as well asnoise, vibration and harshness.

SUMMARY

The present disclosure is directed to a shock absorber which includesvelocity progressive valving for the valve assemblies of the shockabsorber. The valve assemblies are designed to achieve a dampingspecification where the polynomial degree is higher than two. Thevalving system progressively closes the valve with the pressure actionof the damping fluid.

Further areas of applicability will become apparent from the descriptionprovided herein. It should be understood that the description andspecific examples are intended for purposes of illustration only and arenot intended to limit the scope of the present disclosure.

DRAWINGS

The drawings described herein are for illustration purposes only and arenot intended to limit the scope of the present disclosure in any way.

FIG. 1 is a schematic representation of a typical automobile whichincorporates the velocity progressive valving in accordance with thepresent disclosure;

FIG. 2 is a side sectional view of the shock absorber in accordance withthe present disclosure;

FIG. 3 is an enlarged cross-sectional view of the piston assembly inaccordance with the present disclosure;

FIG. 4 is an enlarged view illustrating the velocity progressive valvingconcept of the present disclosure;

FIG. 5 is an enlarged cross-sectional view of the base valve assembly inaccordance with the present disclosure;

FIG. 6 is a graph of a damping curve achievable by the velocityprogressive valving in accordance with the present disclosure;

FIG. 7 is a side sectional view of a shock absorber in accordance withanother embodiment of the present disclosure;

FIG. 8 is an enlarged cross-sectional view of the piston assemblyillustrated in FIG. 7;

FIG. 9 is an enlarged view illustrating a velocity progressive valvingconcept in accordance with another embodiment of the present disclosure;

FIG. 10 is an enlarged view illustrating a velocity progressive valvingconcept in accordance with another embodiment of the present disclosure;

FIG. 11 is a side sectional view of the shock absorber in accordancewith another embodiment of the present disclosure;

FIG. 12 is an enlarged cross-sectional view of the piston assembly inaccordance with the embodiment of the present disclosure illustrated inFIG. 11;

FIGS. 13A and 13B are enlarged views illustrating the velocityprogressive valving concept of the present disclosure;

FIG. 14 is an enlarged cross-sectional view of the base valve assemblyin accordance with the embodiment of the present disclosure illustratedin FIG. 11;

FIG. 15 is a side sectional view of a shock absorber in accordance withanother embodiment of the present disclosure;

FIG. 16 is an enlarged cross-sectional view of the piston assemblyillustrated in FIG. 15;

FIG. 17 is an enlarged view illustrating a velocity progressive valvingconcept in accordance with another embodiment of the present disclosure;

FIG. 18 is an exploded view of the velocity progressive valving conceptillustrated in FIG. 17.

DESCRIPTION

The following description is merely exemplary in nature and is notintended to limit the present disclosure, application, or uses.

Referring now to the drawings in which like reference numerals designatelike or corresponding parts throughout the several views, there is shownin FIG. 1 a vehicle which includes a suspension system incorporating theunique shock absorbers in accordance with the present disclosure andwhich is designated generally by the reference numeral 10. Vehicle 10includes a rear suspension 12, a front suspension 14 and a body 16. Rearsuspension 12 has a transversely extending rear axle assembly (notshown) adapted to operatively support a pair of rear wheels 18 ofvehicle 10. The rear axle assembly is operatively connected to body 16by means of a pair of shock absorbers 20 and a pair of helical coilsprings 22. Similarly, front suspension 14 includes a transverselyextending front axle assembly (not shown) to operatively support a pairof front wheels 24 of vehicle 10. The front axle assembly is operativelyconnected to body 16 by means of a second pair of shock absorbers 26 andby a pair of helical coil springs 28. Shock absorbers 20 and 26 serve todampen the relative motion of the unsprung mass (i.e., front and rearsuspensions 12 and 14, respectively) and the sprung mass (i.e., body 16)of vehicle 10. While vehicle 10 has been depicted as a passenger carhaving front and rear axle assemblies, shock absorbers 20 and 26 may beused with other types of vehicles or in other types of applications suchas vehicles incorporating independent front and/or independent rearsuspension systems. Further, the term “shock absorber” as used herein ismeant to refer to dampers in general and thus will include MacPhersonstruts.

Referring now to FIG. 2, shock absorber 20 is shown in greater detail.While FIG. 2 illustrates only shock absorber 20, it is to be understoodthat shock absorber 26 also includes the unique valve assembly describedbelow for shock absorber 20. Shock absorber 26 only differs from shockabsorber 20 in the manner in which it is adapted to be connected to thesprung and unsprung masses of vehicle 10. Shock absorber 20 comprises apressure tube 30, a piston assembly 32, a piston rod 34, a reservoirtube 36 and a base valve assembly 38.

Pressure tube 30 defines a working chamber 42. Piston assembly 32 isslidably disposed within pressure tube 30 and divides working chamber 42into an upper working chamber 44 and a lower working chamber 46. A seal48 is disposed between piston assembly 32 and pressure tube 30 to permitsliding movement of piston assembly 32 with respect to pressure tube 30without generating undue frictional forces as well as sealing upperworking chamber 44 from lower working chamber 46. Piston rod 34 isattached to piston assembly 32 and extends through upper working chamber44 and through an upper end cap 50 which closes the upper end ofpressure tube 30. A sealing system seals the interface between upper endcap 50, reservoir tube 36 and piston rod 34. The end of piston rod 34opposite to piston assembly 32 is adapted to be secured to the sprungportion of vehicle 10. Valving within piston assembly 32 controls themovement of fluid between upper working chamber 44 and lower workingchamber 46 during movement of piston assembly 32 within pressure tube30. Because piston rod 34 extends only through upper working chamber 44and not lower working chamber 46, movement of piston assembly 32 withrespect to pressure tube 30 causes a difference in the amount of fluiddisplaced in upper working chamber 44 and the amount of fluid displacedin lower working chamber 46. The difference in the amount of fluiddisplaced is known as the “rod volume” and it flows through base valveassembly 38.

Reservoir tube 36 surrounds pressure tube 30 to define a fluid reservoirchamber 52 located between tubes 30 and 36. The bottom end of reservoirtube 36 is closed by an end cap 54 which is adapted to be connected tothe unsprung portion of vehicle 10. The upper end of reservoir tube 36is attached to upper end cap 50. Base valve assembly 38 is disposedbetween lower working chamber 46 and reservoir chamber 52 to control theflow of fluid between chambers 46 and 52. When shock absorber 20 extendsin length, an additional volume of fluid is needed in lower workingchamber 46 due to the “rod volume” concept. Thus, fluid will flow fromreservoir chamber 52 to lower working chamber 46 through base valveassembly 38 as detailed below. When shock absorber 20 compresses inlength, an excess of fluid must be removed from lower working chamber 46due to the “rod volume” concept. Thus, fluid will flow from lowerworking chamber 46 to reservoir chamber 52 through base valve assembly38 as detailed below.

Referring now to FIG. 3, piston assembly 32 comprises a valve body 60and a valve assembly 62. Valve assembly 62 is assembled against ashoulder 66 on piston rod 34. Valve body 60 is assembled against valveassembly 62. A nut 68 secures these components to piston rod 34. Valvebody 60 defines a plurality of fluid passages 70.

Valve assembly 62 comprises a backup washer 80, a valve body 82, a valveguide 84 and a biasing member 86. Backup washer 80 abuts shoulder 66 onpiston rod 34, valve guide 84 abuts backup washer 80, biasing member 86abuts valve guide 84 and valve body 60 abuts biasing member 86. Thisprovides a solid metal connection between nut 68 and shoulder 66 onpiston rod 34 to facilitate the tightening of nut 68.

Valve body 82 is slidingly received on valve guide 84 to move between afirst position abutting backup washer 80 and a second position abuttingvalve body 60. A controlled restriction area 88 is formed between valvebody 82 and valve body 60. Biasing member 86 engages an annular landformed on valve body 82 to bias valve body 82 towards its first positionabutting backup washer 80. Valve body 82 covers the plurality of fluidpassages 70 and when valve body 82 is in its first position abuttingbackup washer 80, the plurality of fluid passages 70 and controlledrestriction area 88 are open. When valve body 82 is in its secondposition abutting valve body 60, the plurality of fluid passages 70 andcontrolled restriction area 88 are closed.

Valve body 82 includes a plurality of flow passages 90 and a pluralityof valve orifices 92. Each of the plurality of flow passages 90 isassociated with and in communication with a respective valve orifice 92to define controlled restriction area 88 as illustrated in FIG. 4. Asealing member or O-ring seals the interface between valve body 82 andpressure tube 30.

As illustrated, biasing member 86 comprises a spacing disc 94, a biasingdisc 96 and a spacing disc 98. Biasing disc 96 is designed to urge valvebody 82 into its first position abutting backup washer 80. While biasingmember 86 is illustrated as discs 94-98, it is within the scope of thepresent invention to utilize other biasing members known in the art.

During a rebound stroke of shock absorber 20, fluid within upper workingchamber 44 flows through the plurality of flow passages 90, theplurality of valve orifices 92, controlled restriction area 88 and fluidpassages 70 into lower working chamber 46. Initially, biasing member 86urges valve body 82 into its first position towards backup washer 80 toopen controlled restriction area 88 and a soft damping load is created.When fluid flow increases with the increase in the velocity of pistonassembly 32, the pressure drop at controlled restriction area 88 willalso increase causing the fluid pressure above valve body 82 to behigher than the fluid pressure below valve body 82. When the resultantforce applied on valve body 82 exceeds the biasing load of biasingmember 86, valve body 82 will begin to move towards its second positionabutting valve body 60. This movement of valve body 82 will reduce thesize of controlled restriction area 88 increasing the damping loadcreated by shock absorber 20. Thus, during a rebound stroke, valve body82 is progressively moving downward with increasing piston velocity.

FIG. 6 illustrates a graph of a damping curve achievable with valveassembly 62. A baseline curve where the force F is equal to kv², apolynomial degree of two, is illustrated as a dashed line. By properlysizing the components of valve assembly 62 including but not limited tothe size of flow passages 90, the size of valve orifices 92, the size ofrestriction area 88 and the load characteristics of biasing member 86, acurve where the polynomial degree is greater than two, as illustrated bythe solid curves, can be achieved with valve assembly 62.

Referring to FIG. 5, base valve assembly 38 comprises a valve body 120and a valve assembly 122. Valve assembly 122 is assembled to valve body120 and a nut 124 secures the two components. Valve body 120 defines aplurality of fluid passages 130.

Valve assembly 122 comprises a backup bolt 140, a valve body 142, and abiasing member 146. Biasing member 146 is disposed between a shoulder onbackup bolt 140 and valve body 120 to provide a metal to metal contactfor facilitate the tightening of nut 124.

Valve body 142 is slidingly received on backup bolt 140 to move betweena first position abutting the flange on backup bolt 140 and a secondposition abutting valve body 120. A controlled restriction area 148 isformed between valve body 142 and valve body 120. Biasing member 146engages an annular land formed on valve body 142 to bias valve body 142towards its first position abutting the flange on backup bolt 140. Valvebody 142 covers the plurality of fluid passages 130 and when valve body142 is in its second position abutting valve body 120, the plurality offluid passages 70 and controlled restriction area 148 are closed.

Valve body 142 includes a plurality of flow passages 150 and a pluralityof valve orifices 152. Each of the plurality of flow passages 150 isassociated with and in communication with a respective valve orifice 152through controlled restriction area 148 as illustrated in FIG. 5. Asealing member or O-ring seals the interface between valve body 142 andpressure tube 30.

As illustrated, biasing member 146 comprises a spacing disc 154, abiasing disc 156 and a spacing disc 158. Biasing disc 156 is designed tourge valve body 142 into its first position abutting backup bolt 140.While biasing member 146 is illustrated as discs 154-158, it is withinthe scope of the present invention to utilize other biasing membersknown in the art.

During a compression stroke of shock absorber 20, fluid within lowerworking chamber 46 flows through the plurality of flow passages 150, theplurality of valve orifices 152, controlled restriction area 148 andfluid passages 130 into reservoir chamber 52. Initially, biasing member146 urges valve body 142 into its first position towards the flange onbackup bolt 140 to open controlled restriction area 148 and a softdamping load is created. When fluid flow increases with the increase inthe velocity of piston assembly 32, the pressure drop at controlledrestriction area 148 will also increase causing the fluid pressure abovevalve body 142 to be higher than the fluid pressure below valve body142. When the resultant force applied on valve body 142 exceed thebiasing load of biasing member 146, valve body 142 will begin to movetowards its second position abutting valve body 120. This movement ofvalve body 142 will reduce the size of controlled restriction area 148increasing the damping load created by shock absorber 20. Thus, during acompression stroke, valve body 142 is moving downward with progressivelyincreasing piston velocity. Valve assembly 122 is thus similar to valveassembly 62 and it can also achieve the damping curve illustrated inFIG. 6.

FIGS. 2-5 illustrate valve assembly 62 of piston assembly 32 and valveassembly 122 of base valve assembly 38 for a dual tube shock absorber.FIGS. 7 and 8 illustrate a monotube shock absorber 220 where two valveassembly 62 are utilized. Shock absorber 220 comprises a pressure tube230, a piston assembly 232 and a piston rod 234.

Pressure tube 230 defines a working chamber 242. Piston assembly 232 isslidably disposed within pressure tube 230 and divides working chamber242 into an upper working chamber 244 and a lower working chamber 246. Aseal 248 is disposed between piston assembly 232 and pressure tube 230to permit sliding movement of piston assembly 232 with respect topressure tube 230 without generating undue frictional forces as well assealing upper working chamber 244 from lower working chamber 246. Pistonrod 234 is attached to piston assembly 232 and extends through upperworking chamber 244 and through an upper end cap 250 which closes theupper end of pressure tube 230. A sealing system seals the interfacebetween upper end cap 250, pressure tube 230 and piston rod 234. The endof piston rod 234 opposite to piston assembly 232 is adapted to besecured to the sprung portion of vehicle 10. Valving within pistonassembly 232 controls the movement of fluid between upper workingchamber 244 and lower working chamber 246 during movement of pistonassembly 232 within pressure tube 230. Because piston rod 234 extendsonly through upper working chamber 244 and not lower working chamber246, movement of piston assembly 232 with respect to pressure tube 230causes a difference in the amount of fluid displaced in upper workingchamber 244 and the amount of fluid displaced in lower working chamber246. The difference in the amount of fluid displaced is known as the“rod volume” is accommodated by a second piston (not shown) disposedwithin pressure tube 230 as is well known in the art.

Referring to FIG. 8, piston assembly 232 comprises a valve body 260 andtwo valve assembly 62. Valve body 260 defines the plurality of fluidpassages 70. Valve assembly 62 is described above and thus it will notbe repeated here. The operation and function of valve assembly 62located above valve body 260 is the same as that described above for arebound stroke for valve assembly 62 and valve body 60. The operationand function of valve assembly 62 located below valve body 260 is thesame as that described above for valve assembly 62 and valve body 60 butbecause this valve assembly 62 is located below valve body 260, itoperates during a compression stroke rather than the rebound strokedescribed above similar to valve assembly 122 described above.

FIG. 9 discloses a piston assembly 332 in accordance with anotherembodiment of the present disclosure is illustrated. Piston assembly 332is similar to piston assembly 32 illustrated in FIG. 3 except that abiasing member 334 is disposed between backup washer 80 and valve guide84. The addition of biasing member 334 facilitates the tightening andretention of nut 68.

As illustrated, biasing member 86 comprises one or more spacing discs 94and one or more biasing discs 96. Biasing discs 96 are designed to urgevalve body 82 into its first position abutting backup washer 80. Whilebiasing member 86 is illustrated as discs 94 and 96, it is within thescope of the present invention to utilize other biasing members known inthe art. Also, valve body 82 illustrated in FIG. 9 includes a land 336which prohibits the full closing of valve body 82 such that a minimumspecified flow will always flow through restriction area 88. A similarland could also be incorporated into the design illustrated in FIGS. 2-7and the design illustrated in FIG. 8. Also, if land 336 is eliminated,valve body 82 would engage valve body 60 to fully close controlledrestriction area 88.

Piston assembly 332 can be substituted for any of the piston assembliesdescribed in this disclosure.

FIG. 10 discloses a piston assembly 432 in accordance with anotherembodiment of the present disclosure is illustrated. Piston assembly 432comprises a valve body 460 and a valve assembly 462. Valve assembly 462is assembled against shoulder 66 on piston rod 34. Valve body 460 isassembled against valve assembly 462. Nut 68 secures these components topiston rod 34. Valve body 460 defines a plurality of fluid passages 470.

Valve assembly 462 comprises a backup washer 480, a valve body 482, atwo-piece valve guide 484 and a biasing member 486. Backup washer 480abuts shoulder 66 on piston rod 34, two-piece valve guide 484 abutsbackup washer 480, biasing member 486 is disposed between the two piecesof two-piece valve guide 484 and valve body 460 abuts two-piece valveguide 484. This provides a solid metal connection between nut 68 andshoulder 66 on piston rod 34 to facilitate the tightening of nut 68.

Valve body 482 is slidingly received on two-piece valve guide 484 tomove between a first position abutting biasing member 486 and a secondposition abutting a spacer 487 disposed between valve body 482 and valvebody 460. A controlled restriction area 488 is formed between valve body482 and valve body 460. Biasing member 486 engages a plurality offingers formed on valve body 482 to bias valve body 482 towards itsfirst position abutting backup washer 480. Valve body 482 covers theplurality of fluid passages 470 and when valve body 482 is in its firstposition abutting biasing member 486, the plurality of fluid passages470 and controlled restriction area 488 are open. When valve body 482 isin its second position abutting spacer 487, the plurality of fluidpassages 470 and controlled restriction area 488 are at their minimumspecified opening which is defined by spacer 487. If spacer 487 isomitted, valve body 482 would abut valve body 460 to close controlledrestriction area 488.

Valve body 482 includes a plurality of flow passages 490 and a pluralityof valve orifices 492. Each of the plurality of flow passages 490 isassociated with and in communication with a respective valve orifice 492to define controlled restriction area 488 as illustrated in FIG. 10. Asealing member or O-ring seals the interface between valve 482 and valvebody 460.

As illustrated, biasing member 486 comprises only a biasing disc 496 butspacing discs 94 and 98 can be included. Biasing disc 496 is designed tourge valve body 482 into its first position abutting biasing member 482.While biasing member 486 is illustrated as disc 496, it is within thescope of the present invention to utilize other biasing members known inthe art.

During a rebound stroke of shock absorber 20, fluid within upper workingchamber 44 flows through the plurality of flow passages 490, theplurality of valve orifices 492, controlled restriction area 488 andfluid passages 470 into lower working chamber 46. Initially, biasingmember 486 urges valve body 482 into its first position towards biasingmember 486 to open controlled restriction area 488 and a soft dampingload is created. When fluid flow increases with the increase in thevelocity of piston assembly 432, the pressure drop at controlledrestriction area 488 will also increase causing the fluid pressure abovevalve 482 to be higher than the fluid pressure below valve body 482.When the resultant force applied on valve body 482 exceed the biasingload of biasing member 486, valve body 482 will begin to move towardsits second position abutting spacer 487. This movement of valve body 482will reduce the size of controlled restriction area 488 increasing thedamping load created by shock absorber 20. Thus, during a reboundstroke, valve body 482 is progressively moving downward with increasingpiston velocity. Piston assembly 432 can be substituted for any of thepiston assemblies described in this disclosure.

Referring now to FIG. 11, shock absorber 520 is shown in greater detail.While FIG. 11 illustrates only shock absorber 520, it is to beunderstood that shock absorber 26 could also includes the unique valveassembly described below for shock absorber 520. Shock absorber 26 onlydiffers from shock absorber 520 in the manner in which it is adapted tobe connected to the sprung and unsprung masses of vehicle 10. Shockabsorber 520 comprises a pressure tube 530, a piston assembly 532, apiston rod 534, a reservoir tube 536 and a base valve assembly 538.

Pressure tube 530 defines a working chamber 542. Piston assembly 532 isslidably disposed within pressure tube 530 and divides working chamber542 into an upper working chamber 544 and a lower working chamber 546. Aseal 548 is disposed between piston assembly 532 and pressure tube 530to permit sliding movement of piston assembly 532 with respect topressure tube 530 without generating undue frictional forces as well assealing upper working chamber 544 from lower working chamber 546. Pistonrod 534 is attached to piston assembly 532 and extends through upperworking chamber 544 and through an upper end cap 550 which closes theupper end of pressure tube 530. A sealing system seals the interfacebetween upper end cap 550, reservoir tube 536 and piston rod 534. Theend of piston rod 534 opposite to piston assembly 532 is adapted to besecured to the sprung portion of vehicle 10. Valving within pistonassembly 532 controls the movement of fluid between upper workingchamber 544 and lower working chamber 546 during movement of pistonassembly 532 within pressure tube 530. Because piston rod 534 extendsonly through upper working chamber 544 and not lower working chamber546, movement of piston assembly 532 with respect to pressure tube 530causes a difference in the amount of fluid displaced in upper workingchamber 544 and the amount of fluid displaced in lower working chamber546. The difference in the amount of fluid displaced is known as the“rod volume” and it flows through base valve assembly 538.

Reservoir tube 536 surrounds pressure tube 530 to define a fluidreservoir chamber 552 located between tubes 530 and 536. The bottom endof reservoir tube 536 is closed by an end cap 554 which is adapted to beconnected to the unsprung portion of vehicle 10. The upper end ofreservoir tube 536 is attached to upper end cap 550. Base valve assembly538 is disposed between lower working chamber 546 and reservoir chamber552 to control the flow of fluid between chambers 546 and 552. Whenshock absorber 520 extends in length, an additional volume of fluid isneeded in lower working chamber 546 due to the “rod volume” concept.Thus, fluid will flow from reservoir chamber 552 to lower workingchamber 546 through base valve assembly 538 as detailed below. Whenshock absorber 520 compresses in length, an excess of fluid must beremoved from lower working chamber 546 due to the “rod volume” concept.Thus, fluid will flow from lower working chamber 546 to reservoirchamber 552 through base valve assembly 538 as detailed below.

Referring now to FIG. 12, piston assembly 532 comprises a valve body 560and a valve assembly 562. Valve assembly 562 is assembled against ashoulder 566 on piston rod 534. Valve body 560 is assembled againstvalve assembly 562. A nut 568 secures these components to piston rod534. Valve body 560 defines a plurality of fluid passages 570.

Valve assembly 562 comprises a backup washer 580, one or more spacerdiscs 582, one or more pilot discs 584 and one or more main discs 586.Backup washer 580 abuts shoulder 566 on piston rod 534, the one or morespacer discs 582 abut backup washer 580, the one or more pilot discs 584abut spacer discs 582, the one or more main discs 586 abut pilot discs584 and valve body 560 abuts main discs 586. This provides a solid metalconnection between nut 568 and shoulder 566 on piston rod 534 tofacilitate the tightening of nut 568.

The pilot disc 584 immediately adjacent valve body 560 engages a pistonland 590 formed on valve body 560. The pilot disc 584 engaging pistonland 590 defines one or more notches 592 which enable fluid flow pastpiston land 590. The main disc 586 immediately adjacent valve body 560engages a piston land 594 formed on valve body 560. The main disc 586engaging piston land 594 defines one or more notches 596 which enablefluid flow past piston land 594. A controlled restriction area 598 isformed between pilot discs 584 and main discs 586 as is illustrated inFIG. 13A. Fluid is allowed to flow both axially and radially through theone or more notches 596 as illustrated in FIG. 13A.

During a rebound stroke of shock absorber 520, fluid within upperworking chamber 544 flows through the one or more notches 592, axiallyand radially through the one or more notches 596 and through passages570 into lower working chamber 546. Initially, there is no deflection ofthe one or more pilot discs 584 and controlled restriction area 598 isopen to allow for the axial and radial flow through the one or morenotches 596 to produce a relatively soft damping load. When fluid flowincreases with the increase in the velocity of piston assembly 532, thepressure drop at controlled restriction area 598 will increase causingthe fluid pressure above the one or more pilot discs 584 to be higherthan the fluid pressure below the one or more pilot discs 584. When theresultant force applied on the one or more pilot discs 584 exceeds theload required to deflect the one or more pilot discs 584, the one ormore pilot discs 584 will deflect towards valve body 560 to close theaxial pathway through the one or more notches 596 as illustrated in FIG.13B. This deflection of the one or more pilot discs 584 will reduce thesize of controlled restriction area 598 by eliminating the axial flowthrough the one or more notches 596 leaving only the radial flowincreasing the damping load created by shock absorber 520. Thus, duringa rebound stroke, the one or more pilot discs 584 progressively movedownward with increasing piston velocity. The thickness of the one ormore main discs will determine the minimum specified flow through theone or more notches 596. Valve assembly 562, similar to valve assembly62, can also achieve the damping curve illustrated in FIG. 6.

Referring to FIG. 14, base valve assembly 538 comprises a valve body 620and a valve assembly 622. Valve assembly 622 is assembled to valve body620 and a nut 624 secures the two components. Valve body 620 defines aplurality of fluid passages 628.

Valve assembly 622 comprises a backup bolt 640, one or more spacer discs582, one or more pilot discs 584 and one or more main discs 586. The oneor more spacer discs 582 abut backup bolt 640, the one or more pilotdiscs 584 abut spacer discs 582, the one or more main discs 586 abutpilot discs 584 and valve body 620 abuts main discs 586. This provides asolid metal connection between nut 624 and the head on backup bolt 640to facilitate the tightening of nut 624.

The pilot disc 584 immediately adjacent valve body 620 engages a pistonland 630 formed on valve body 620. The pilot disc 584 engaging pistonland 630 defines one or more notches 632 which enable fluid flow pastpiston land 630. The main disc 586 immediately adjacent valve body 620engages a piston land 634 formed on valve body 620. The main disc 586engaging piston land 634 defines one or more notches 636 which enablefluid flow past piston land 634. A controlled restriction area 638 isformed between pilot discs 584 and main discs 586 similar to restrictionarea 598 illustrated in FIG. 13A. Fluid is allowed to flow both axiallyand radially through the one or more notches 636 the same as notches 596illustrated in FIG. 13A.

During a compression stroke of shock absorber 520, fluid within lowerworking chamber 546 flows through the one or more notches 632, axiallyand radially through the one or more notches 636 and through passages628 into reservoir chamber 552. Initially, there is no deflection of theone or more pilot discs 584 and controlled restriction area 638 is opento allow for the axial and radial flow through the one or more notches636 to produce a relatively soft damping load. When fluid flow increaseswith the increase in the velocity of piston assembly 532, the pressuredrop at controlled restriction area 638 will increase causing the fluidpressure above the one or more pilot discs 584 to be higher than thefluid pressure below the one or more pilot discs 584. When the resultantforce applied on the one or more pilot discs 584 exceeds the loadrequired to deflect the one or more pilot discs 584, the one or morepilot discs 584 will deflect towards valve body 620 to close the axialpathway through the one or more notches 636 similar to notches 596illustrated in FIG. 13B. This deflection of the one or more pilot discs584 will reduce the size of controlled restriction area 638 byeliminating the axial flow through the one or more notches 636 leavingonly the radial flow increasing the damping load created by shockabsorber 520. Thus, during a compression stroke, the one or more pilotdiscs 584 progressively move downward with increasing piston velocity.The thickness of the one or more main discs will determine the minimumspecified flow through the one or more notches 596. Valve assembly 622,similar to valve assembly 62, can also achieve the damping curveillustrated in FIG. 6.

FIGS. 11-14 illustrate valve assembly 562 of piston assembly 532 andvalve assembly 622 of base valve assembly 538 for a dual tube shockabsorber. FIGS. 15 and 16 illustrate a monotube shock absorber assembly720 where two valve assembly 562 are utilized. Shock absorber 720comprises a pressure tube 730, a piston assembly 732 and a piston rod734.

Pressure tube 730 defines a working chamber 742. Piston assembly 732 isslidably disposed within pressure tube 730 and divides working chamber742 into an upper working chamber 744 and a lower working chamber 746. Aseal 748 is disposed between piston assembly 732 and pressure tube 730to permit sliding movement of piston assembly 732 with respect topressure tube 730 without generating undue frictional forces as well assealing upper working chamber 744 from lower working chamber 746. Pistonrod 734 is attached to piston assembly 732 and extends through upperworking chamber 744 and through an upper end cap 750 which closes theupper end of pressure tube 730. A sealing system seals the interfacebetween upper end cap 750, pressure tube 730 and piston rod 734. The endof piston rod 734 opposite to piston assembly 732 is adapted to besecured to the sprung portion of vehicle 10. Valving within pistonassembly 732 controls the movement of fluid between upper workingchamber 744 and lower working chamber 746 during movement of pistonassembly 732 within pressure tube 730. Because piston rod 734 extendsonly through upper working chamber 744 and not lower working chamber746, movement of piston assembly 732 with respect to pressure tube 730causes a difference in the amount of fluid displaced in upper workingchamber 744 and the amount of fluid displaced in lower working chamber746. The difference in the amount of fluid displaced is known as the“rod volume” is accommodated by a second piston (not shown) disposedwithin pressure tube 730 as is well known in the art.

Referring to FIG. 16, piston assembly 732 comprises a valve body 760 andtwo valve assembly 562. Valve body 760 defines the plurality of fluidpassages 570. Valve assembly 562 is described above and thus it will notbe repeated here. The operation and function of valve assembly 562located above valve body 760 is the same as that described above for arebound stroke for valve assembly 562 and valve body 560. The operationand function of valve assembly 562 located below valve body 760 is thesame as that described above for valve assembly 562 and valve body 560but because this valve assembly 562 is located below valve body 760, itoperates during a compression stroke rather than the rebound strokedescribed above similar to valve assembly 622 described above.

FIGS. 17 and 18 discloses a piston assembly 832 in accordance withanother embodiment of the present disclosure is illustrated. Pistonassembly 832 is similar to piston assembly 732 illustrated in FIG. 16except that a biasing member 834 is disposed between back-up washer 580and spacer disc 582 for both rebound and compression valving. Theaddition of biasing member 834 facilitates the tightening and retentionof nut 568. Piston assembly 832 can be substituted for any of the pistonassemblies described in this disclosure.

What is claimed is:
 1. A shock absorber comprising: a pressure tubeforming a working chamber; a piston body disposed within said workingchamber formed by said pressure tube, said piston body dividing saidworking chamber into an upper working chamber and a lower workingchamber, said piston body defining a passage extending between saidupper working chamber and said lower working chamber; a piston rodattached to said piston body, said piston rod extending through one endof said pressure tube; a first valve assembly engaging said piston body,said first valve assembly comprising: a first biasing member engagingsaid piston body; and a first valve engaging said first biasing member,said first valve moving axially with respect to said piston rod, saidfirst biasing member urging said first valve away from said piston body.2. The shock absorber according to claim 1, wherein said first biasingmember includes a disc spring.
 3. The shock absorber according to claim1, wherein said first valve defines a valve orifice in communicationwith said passage in said piston body.
 4. The shock absorber accordingto claim 1, wherein said first valve and said piston body define acontrolled restriction, said controlled restriction reducing in sizewhen said piston body moves axially within said pressure tube.
 5. Theshock absorber according to claim 1, wherein said first valve sealinglyengages said pressure tube.
 6. The shock absorber according to claim 1,further comprising a first valve guide disposed between said piston rodand said first valve.
 7. The shock absorber according to claim 6,wherein said first biasing member is disposed between said piston rodand said first valve guide.
 8. The shock absorber according to claim 1,wherein an outer circumference of said first valve sealingly engagessaid piston body.
 9. The shock absorber according to claim 1, whereinthe shock absorber further comprises a second valve assembly, saidsecond valve assembly comprising: a second biasing member engaging saidpiston body; a second valve engaging said second biasing member, saidsecond valve moving axially with respect to said piston rod, said secondbiasing member urging said second valve away from said piston body. 10.The shock absorber according to claim 9, wherein said first and secondbiasing members include a disc spring.
 11. The shock absorber accordingto claim 9, wherein each of said first and second valves define a valveorifice in communication with said passage in said piston body.
 12. Theshock absorber according to claim 9, wherein each of said first andsecond valves and said piston body define a controlled restriction, eachof said controlled restrictions reducing in size when said piston bodymoves axially within said pressure tube.
 13. The shock absorberaccording to claim 9, wherein each of said first and second valvessealingly engage said pressure tube.
 14. The shock absorber according toclaim 9, further comprising a first valve guide disposed between saidpiston rod and said first valve and a second valve guide disposedbetween said piston rod and said second valve.
 15. The shock absorberaccording to claim 14, wherein said first biasing member is disposedbetween said piston rod and said first valve guide and said secondbiasing member is disposed between said piston rod and said second valveguide.
 16. The shock absorber according to claim 9, wherein an outercircumference of each of said first and second valves sealingly engagessaid piston body.
 17. The shock absorber according to claim 1, furthercomprising: a reserve tube surrounding said pressure tube to define areserve chamber; a base valve assembly disposed between said workingchamber and said reserve chamber, said base valve assembly comprising: abase valve body defining a passage extending between said workingchamber and said reserve chamber; a second biasing member engaging saidbase valve body; and a second valve engaging said second biasing member,said second valve moving axially with respect to said base valve body,said second biasing member urging said second valve away from said basevalve body.
 18. The shock absorber according to claim 17, wherein saidfirst and second biasing members include a disc spring.
 19. The shockabsorber according to claim 17, wherein said first valve defines a firstvalve orifice in communication with said passage in said piston body andsaid second valve defines a second orifice in communication with saidpassage in said base valve body.
 20. The shock absorber according toclaim 17, wherein said first valve and said piston body define a firstcontrolled restriction, said first controlled restriction reducing insize when said piston body moves axially within said pressure tube, saidsecond valve and said base valve body define a second controlledrestriction, said second controlled restriction reducing in size whensaid piston body moves axially within said pressure tube.
 21. The shockabsorber according to claim 17, wherein each of said first and secondvalves sealingly engage said pressure tube.
 22. The shock absorberaccording to claim 17, further comprising a first valve guide disposedbetween said piston rod and said first valve and a second valve guidedisposed between said base valve body and said second valve.
 23. Theshock absorber according to claim 22, wherein said first biasing memberdisposed between said piston rod and said first valve guide and saidsecond biasing member disposed between said base valve body and saidsecond valve guide.
 24. The shock absorber according to claim 17,wherein an outer circumference of said first valve sealingly engagessaid piston body and an outer circumference of said second valvesealingly engages said base valve body.